Recent results on correlations and fluctuations in $p p$, $p$ +Pb, Pb+Pb and Xe+Xe collisions from the ATLAS Experiment at the LHC

Abstract

The azimuthal anisotropies of particle yields observed in relativistic heavy-ion collisions have been traditionally considered as a strong evidence of the formation of a de-confined quark-gluon plasma produced in these collisions. However multiple recent measurements from the LHC experiments in $pp$ and $p$+Pb systems show similar features as those observed in Pb+Pb collisions, indicating the possibility of the production of such a de-confined medium also in smaller collision systems. This report presents a comprehensive summary of recent ATLAS measurements in $pp$ and $p$+Pb collisions as well as in Pb+Pb and Xe+Xe collisions. It includes measurements of two-particle hadron-hadron correlations in $\Delta\phi$ and $\Delta\eta$, with a template fitting procedure used to subtract the dijet contributions. Measurements of multi-particle cumulants using the standard cumulant method as well as a new sub-event cumulant method that suppresses the contribution of non-flow effects are discussed. Studies of longitudinal flow decorrelation and correlations between flow harmonics and mean $p_\mathrm{T}$ of the event in Pb+Pb collisions are presented to provide deeper insight into details of the geometry of the initial state. First results on flow harmonic measurements from Xe+Xe collisions are also discussed.